Tegner said the liquid smelled like urine and it was "all over him," and said Cavendish talked about the incident after completing the time trial.

"He said: 'I really don't know what's going on,'" Tegner said.

Tegner said the team does not know exactly where it happened on the 33-kilometer (20-mile) time-trial course to Mont-Saint-Michel on the Brittany coast.

The Guardian, on its website, quoted team manager Patrick Lefevere as saying: "Mark is sad, he's not upset, just sad. I cannot blame anyone, there are 100,000 or 200,000 people on the road, and one person decided to do this."

At the Tour, which is a free, non-ticketed event, the millions of roadside fans get closer to the athletes than at many other sports competitions. Most famously, a spectator once punched five-time champion Eddy Merckx in the kidneys.

Lance Armstrong tweeted: "why all the sudden shock and outrage. this has been happening for 100 years in some form or another."